A former international representative rugby league and rugby union player – a dual-code international – Stuart also played State of Origin for New South Wales in the first Gould era. At club level, Stuart was the half-back of the "Green Machine", the Canberra Raiders team that won three premierships in 1989, 1990 and 1994 and were runners-up in 1991 who were coached by Tim Sheens. As a player Stuart was noted for his ability to throw long, spiralling passes to both the left and right sides of the field.[4]

Stuart then switched codes to league and joined the Canberra Raiders team in 1988, winning the club's player of the year award that season. He was a key member of the club's most successful period in the late 1980s and early 1990s, playing halfback inside a backline including legendary talents Laurie Daley, Mal Meninga and Gary Belcher. Stuart would go on to win three premierships with the Canberra Raiders. After the 1989 Grand Final victory, Stuart travelled to England with the Raiders for the 1989 World Club Challenge which was lost to Widnes.

Stuart was named man-of-the-match in the second game of the 1990 State of Origin series. He won the Clive Churchill Medal in the Raiders' 1990 grand final victory. He debuted in the first test of the 1990 Kangaroo tour against Great Britain in London in October 1990, playing five-eighth outside Alan Langer. This appearance saw him become Australia's 38th dual code rugby international, following Michael O'Connor and preceding Scott Gourley. He replaced Langer at halfback in the next test. In 1992 and 1993 Stuart was again named the Raiders' player of the year and in 1993 Stuart won the Dally M Medal for the Winfield Cup's Player of the Year. He went on the 1994 Kangaroo Tour and his first test of the tour was the 2nd test. He was again preceded by Langer.

Stuart began his first grade coaching career in 2002 with the Sydney Roosters, taking over from Graham Murray and winning the premiership in his first year as coach. Having won the 2002 NRL Premiership, the Roosters traveled to England to play the 2003 World Club Challenge against Super League champions, St Helens RLFC. Stuart coached Sydney to a 38-0 victory. That year he took the Roosters to the 2003 NRL grand final but they lost to the Penrith Panthers. The 2004 Stuart-coached Roosters side was also beaten in the Grand Final, but the team struggled in 2005 and 2006 despite the high calibre of the player roster. Stuart's contract was terminated and he left the Roosters two weeks before the end of the 2006 season.

But on 24 May 2010, with 18 months left on his contract, Stuart announced his resignation from the end of the 2010 season,ending yet another tenure prematurely and at loggerheads with club executives,members and players, handing the job over to current Sharks coach, Shane Flanagan.[6]

Despite the Sharks making the preliminary finals in 2008, Stuart's time with the club was marred by a horror year in 2009. Not only was the club in dire financial straits [7] but the Cronulla Sharks club was also tarnished by media allegations about a 2002 group-sex incident involving former Sharks players, player Reni Maitua's dismissal after testing positive to drugs,[8] removal of the captaincy from key player Paul Gallen, due to making racist remarks several unsavoury incidents involving now-disgraced CEO Tony Zappia (including his assault of a female staff member and involvement in an insurance-fraud fan donation scandal).[9]

Stuart signed a lucrative three-year contract with the Parramatta Eels, beginning in 2013. This meant that Stuart had to stand down as the head coach of the New South Wales State of Origin team, as the state had put in a policy that the head coach would not have any relation to an NRL club. The Eels had in recent years been perennial underachievers, with Stuart set the unenviable task of resurrecting the team after the team finished last in 2012. However, in the round 4 match against the Roosters, Stuart suffered the worst defeat in his NRL coaching career, losing 50-0.[10]

In April 2013 Stuart was fined $10,000 for questioning a referee's impartiality following a loss to the Gold Coast.[11]

On 11 September 2013, Stuart announced that he was quitting the Parramatta Eels to join the Canberra Raiders as head coach on a three-year contract to continue his coaching career.[12]

In 2005, Stuart was appointed coach of the New South Wales. His coaching approach continued the Phil Gould legacy of matching the Queensland passion by focussing the NSW players' pride in the jumper and achievements of those who have worn it before. Although Stuart only coached the NSW side for just one series, the Blues managed to win the series 2-1 after losing the first match in golden point. On 17 November 2010 Stuart was appointed as the state's first full-time coach of the New South Wales State of Origin team for two years with a get-out clause for the 2012 series should Stuart return to NRL coaching.[citation needed] Stuart's victory in 2005 was the last time NSW won an origin series until the Laurie Daley coached Blues won in 2014.

Stuart coached the Blues for the 2011 series, which was lost to the Maroons by two games to one.

Stuart continued in the NSW head coaching role for the 2012 series, which was once again lost by two games to one. For the second consecutive year however, New South Wales won Game II in Sydney. Shortly after signing on as Parramatta Eels coach for the 2013 season onwards, Stuart resigned from his role as NSW coach.[14]

In December 2005 Stuart was appointed as coach of Australian national rugby league team, replacing Wayne Bennett after Australia's loss in the 2005Tri-Nations final to New Zealand by a scoreline of 24-0.[15] This meant that Stuart had to stand down as coach of the New South Wales State of Origin team. Stuart enjoyed success with the Kangaroos: winning the Anzac Tests of 2006 and 2007, as well as the 2006 Tri-Nations. In addition, at the end of the 2007 season, the team won a one-off Test against New Zealand.

Stuart's Australian team lost the 2008 Rugby League World Cup final to New Zealand, 34–20. Afterwards he was reported to be so incensed by the defeat that he verbally attacked Geoff Carr, the Chief Executive of Australian Rugby League, claiming that tournament organizers and match officials conspired to cause the Australian loss.[16] The next morning he had a chance meeting with Ashley Klein, who refereed the final, and Stuart Cummings, England's director of referees, at their hotel. He is reported to have verbally abused both officials in front of a number of witnesses, calling Klein a cheat, and of being physically and aggressively intimidating.[17]